1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer.
2. Description of the Related Art
There is known an image forming apparatus as an apparatus in which a toner image formed on a photoconductive drum is transferred to a sheet of recording paper so as to form an image on the sheet of recording paper. Conventionally, an image forming apparatus capable of obtaining high quality printed image is desired.
FIG. 6A and FIG. 6B show part of an image forming apparatus 1 in accordance with the conventional technique. FIG. 6A is a cross sectional view and FIG. 6B shows a simplified model. As shown in FIG. 6A, a photoconductive drum 2 is composed of a hollow cylindrical photoconductive drum elementary pipe portion 43 and a pair of drum flanges 6 which cover openings at both ends of the photoreceptor drum elementary pipe portion 43. Further, a drum shaft 8, which penetrates the photoconductive drum 2 in the axial direction, is provided on the same shaft as that of the photoconductive drum 2. Then, the drum shaft 8 is rotatably supported by a pair of shaft bearings 41 provided at both ends of the drum shaft.
A transfer roller 3 has a cylindrical shape, and an axis A2 thereof is arranged in parallel with an axis A1 of the photoconductive drum 2. Further, a roller shaft 7, which penetrates the transfer roller 3 in the axial direction, is provided on the same shaft as that of the transfer roller 3, and is rotatably supported by a pair of shaft bearings 42 provided at both ends of the roller shaft. Further, the roller shaft 7 comes in contact with a pair of spring members 5 having elasticity in the axial direction, a pair of tracking rolls 4, which are a control means according to the invention, are provided. The roller shaft 7 is pressed against the drum shaft 8 with the spring members 5. The gap H is made between the photoconductive drum 2 and the transfer roller 3 at a proper value by allowing each tracking roll 4 to come in contact with the photoconductive drum 2. Such conventional image forming apparatus 1 is disclosed in Japanese Unexamined Patent Publication JP-A 9-218549 (1997).
Such an image forming apparatus 1 is configured to make the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller. Accordingly, the photoconductive drum and the transfer roller can move without friction, so that abrasion and peeling of the photoreceptive layer in the circumferential surface of the photoreceptor drum can be prevented. Consequently, the toner image can be finely transferred to the recording paper, thereby preventing fluctuation of image.
Further, in addition to the above mentioned image forming apparatus which is configured to keep the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller at a proper value by the controlling means such as a tracking roll, there is another image forming apparatus, which is configured so as to press the circumferential surface of the photoconductive drum and the circumferential surface of the transfer roller with a specific pressure by the controlling means. Such conventional technique is disclosed in Japanese Unexamined Patent Publication JP-A 2-165173 (1990).
According to the image forming apparatus, by bringing the circumferential surface of the photoconductive drum into contact with the circumferential surface of the transfer roller, and by pressing them at a steady specific pressure, there is no need to further increase the transfer electric field (or potential difference) which functions between the circumferential surface of the photoconductive drum and the circumferential surface of the transfer drum. Further, problems such that letters are missing in the middle part due to high pressure is not raised. Consequently, the toner image can be finely transferred to the recording paper.
The foregoing conventional technique has the following problems, in which the positional relationship between the outer circumference of an image carrier which supports a toner image, such as a photoconductive drum, a photoconductor belt, and an intermediate transfer, and the circumferential surface of the transfer roller which transfers the toner image on the image carrier to the recording paper, is controlled to be a predetermined positional relationship by spring members and the controlling means.
When inserting a sheet of recording paper between the surface of the image carrier and the surface of the transfer roller, the interval between the photoconductive drum and the transfer roller further increases in comparison with the case where sheets of recording paper are not housed in the space between the surface of the image carrier and the surface of the transfer roller. After discharging the recording paper from the space between the surface of image carrier and the surface of the transfer roller, the positional relationship is reset to its original position by the spring members. At the time, an impact caused by insertion and withdrawal of the recording paper, is transmitted to the image carrier. In particular, when inserting a recording paper having a certain thickness and unevenness, the impact is increased.
An impact is transmitted to the image carrier, thereby causing displacement of the image carrier in a short time and creating vibrations on the toner image supported on the image carrier and unfixed toner image which is transferred to the recording paper. Consequently, there is problems that blot and blur of image are generated due to vibrations and high quality image cannot be obtained. In a particular case where the image carrier and the transfer roller have a hollow, when an impact is transmitted to the outer circumference of the portion having a hollow inside, vibrations created by the image carrier is further increased.
Further, according to the copying machine, which is one example of the image forming apparatus, after fixing an image of a developing material such as a toner on the circumferential surface of the photoconductive drum, which is one example of the image carrier, the toner image is transferred to transfer materials such as a transfer sheet, thereby printing the image. At the time, in the periphery of the photoconductive drum, rotating bodies are provided, namely, a charging roller which applies static charges to the photoconductive drum, a developing roller which forms a toner image on the circumferential surface of the photoconductive drum, and a transfer roller which transfers the toner image by pressing against the circumference of the photoconductive drum. At this time, to obtain an image having a certain quality, these rotating bodies provided in the periphery are required to keep the interval between shafts or the interval between circumferential surfaces with regard to the photoconductive drum with high accuracy.
In response to the needs, the following technique is proposed in, for example, JP-A 2-165173 and Japanese Unexamined Patent Publication JP-A 8-63043 (1996). A guide portion is provided on the peripheral rotating body such as the transfer roller and the circumference or the rotation axis of the image carrier such as the photoconductive drum, and the guide portion comes in contact with the circumference of the image carrier or the peripheral rotating body, thereby keeping the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences to a proper value.
Further, according to the technique disclosed in Japanese Unexamined Patent Publication JP-A 4-175779 (1992), a ring-shaped spacer roller provided on the peripheral rotating body are brought into contact with support members of the image carrier, thereby the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences can be kept to a proper value.
In JP-A 2-165173 and JP-A 8-63043, the following technique is disclosed. The guide portion or the like comes in contact with the opposing material while rotating around the periphery of each rotating shaft in accordance with the rotation of the image carrier and the peripheral rotating body. In JP-A 4-175779, the spacer roller are brought in contact with a supporting portion of the image carrier while rotating in accordance with the rotation of the support member of the image carrier and the peripheral rotating body.
Then, in the periphery of the image carrier, fine particles made of the developing material such as a toner, and the transfer material such as a transfer sheet, are suspended in general. In such environment, there is a problem in accordance with the technique disclosed in JP-A 2-165173 and JP-A 8-63043. Because the guide portion comes in contact with the opposing material while rotating, the particles bite the contact surface, thereby creating vibrations on the image carrier and the peripheral rotating body, or causing the abrasion on the contact surface. Consequently, it becomes difficult to keep the interval between the image carrier and the peripheral rotating body to a proper value, in some cases. Further, according to JP-A 4-175779, since the support member of the image carrier to be contacted with the spacer roller is generally charged, it can relieve adhesion of the toner or the like, however, it is impossible to solve the problem of the abrasion. Moreover, the guide portion disclosed in JP-A 2-165173 and JP-A 8-63043, and the spacer roller disclosed in JP-A 4-175779, the whole circumferences become the contact surface. Therefore, there is necessity to process the whole circumferences of the guide portion and the spacer in high accuracy, so that the cost of processing rises.
Further, according to the copying machine, which is one example of the image forming apparatus, to transfer a toner image formed on the circumference of the photoconductive drum (an example of an image carrier), to a paper or the like (an example of a transfer material), the paper is guided to the predetermined transfer position by a paper guide (an example of a guide member) in close proximity to the transfer roller (an example of a transfer member). The paper or the like is pressed against part of the circumferential surface of rotating photoreceptor drum by the transfer roller, thereby transferring the toner image. At the time, to keep a certain image quality of the transferring image transferred to the paper or the like, the transfer roller and the paper guide should be arranged with respect to the photoreceptor drum with high accuracy.
Then, when a paper jam is caused between the transfer roller and the photoreceptor drum or the paper guide, or when a stain is found on the circumferential surface of the transfer roller, it is necessary to remove the jammed paper or perform maintenance such as cleaning of the circumferential surface of the transfer roller. Because of this, the transfer roller and the paper guide, which is formed in close proximity thereto, should be supported to be separated. Also, it is desirable to perform the separation easily. To meet the needs, the following technique is disclosed in Japanese Unexamined Patent Publication JP-A 11-93940 (1999). As a method of supporting the transfer roller so as to facilitate a work top mount and demount, mounting and demounting of the transfer roller can be easily carried out by providing a collar, a handle part, and the like provided with a small-diameter part in a non-circular shape in cross section, at the end portion of the rotation axis of the transfer roller, and rotating the small-diameter part in the direction capable of mounting and demounting through operation of the handle part.
According to JP-A 11-93940, however, when mounting and demounting the transfer roller at the time of performing maintenance, the paper guide should be mounted and demounted with a screw and the like, so that there is a problem that it takes much time to perform maintenance operation. Moreover, there arises another problem that the extent of screwing causes displacement of the positional relationship between the transfer roller and the paper guide.
According to the copying machine and the like, which is one example of the image forming apparatus, to transfer a toner image formed on the circumferential surface of the photoconductive drum (an example of an image carrier), to a paper or the like (an example of a transfer material), the paper is guided to the predetermined transfer position by a paper guide (an example of a guide member) in close proximity to the transfer roller (an example of a transfer member). The paper is pressed against part of the circumferential surface of rotating photoconductive drum by the transfer roller, thereby transferring the toner image. Further, the paper which is stuck to the photoconductive drum due to static electricity, is peeled off by removing static electricity from the transferred paper, with a means for removing static. At the time, to keep a certain image quality of the transferring image transferred to the paper, the interval between the transfer roller or the paper guide and the means for removing static should be arranged with respect to the photoreceptor drum with high accuracy. In addition to this, the intense of pressing the transfer member against the photoconductive drum should be kept consistently. To meet the needs, the following technique is disclosed in Japanese Examined Patent Publication JP-B2 2710996. By supporting the paper guide with a shaft of the transfer roller, the paper guide is arranged with respect to the transfer roller with high accuracy.
In general, the transfer member such as a transfer roller is pressed against the image carrier with a spring or the like so as to keep consistent intense of pressing against the image carrier. Accordingly, when the surface of the transfer member deteriorates with time, the position of the rotation axis of the transfer member with respect to the image carrier is deviated. At the time, since the paper guide is supported with the shaft of the transfer roller according to JP-B2 2710996, there is a problem that the position of the paper guide with respect to the image carrier is also deviated. Further, when performing maintenance on the transfer roller at paper jam, it is necessary to remove the paper guide from the shaft of the transfer roller. However, the function of facilitating the removal is not indicated, so that there is a problem that maintenance operation is difficult.
Moreover, the function for positioning of the means for removing static electricity is not particularly disclosed in JP-B2 2710996. It can be considered to support the means for removing static electricity with a shaft of the transfer roller, as in the case of supporting the paper guide disclosed in JP-B2 2710996, however, there is a problem that the position is deviated when the surface of the transfer roller deteriorates with time.
It is an object of the invention to provide an image forming apparatus in which fine transfer can be carried out without transmitting vibrations to an image carrier and a recording paper even if an impact is caused when inserting and discharging the recording paper.
It is an object of the invention to provide an image forming apparatus at low cost, in which proper positioning can be carried out without causing vibrations due to a bite of suspended particles such as a toner or the abrasion of the members for positioning.
It is an object of the invention to provide an image forming apparatus in which positioning of the transfer member and the guide member which guides a transfer material to the transfer position, can be carried out with respect to the image carrier with high accuracy, and the guide members, which are arranged in close proximity to the transfer member, can be easily separated so as to perform maintenance on the transfer member.
It is an object of the invention to provide an image forming apparatus which facilitates the positioning of the transfer member, the guide member, the means for removing static electricity, and the like, with respect to the image carrier with high accuracy.